The Human
Body
5
The Nervous System
NPS/NAFL NORTH
NPSNAFLNORTH|
KOCL|May2021
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Contents
The Human Body Page 3
The Brain Page 7
Spinal Cord Page 11
Nerves Page 12
Reflex Actions Page 15
Sense Organs Page 17
Be Good to Your Brain Page 25
Keep in Mind Page 26
Vocabulary Page 27
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The human body is a wonderfully efficient and complex machine. It
has organs and systems that are organized to perform specific
functions. The stomach, the intestines, the liver and the pancreas
help in the digestion of food and constitute the digestive system.
The lungs help in breathing and make up the respiratory system. The
system that helps you feel and react is the nervous system. The
system that helps in movement is the locomotory/muscular system.
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THE HUMAN BODY
Have you ever wondered why you never
feel any sensation when you cut your
nails or hair but feel pain when you get a
cut on your finger?
When a message reaches the brain from
any part of the body, the brain interprets
it and tells the body how to react.
For example, if you accidentally cut your
finger on a sharp object, special cells
called nerve cells that are present in your
skin, shoot a message of pain to your
brain. The brain tells you to pull your
hand away. This happens because of the
functioning nervous system in your body.
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Nerve
Cells
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NERVE CELLS
Brain
Spinal
cord
Wizard’s Corner
Messages travel along the large nerves, at a
speed of more than 90 metres per second.
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Neurons receive messages from the
outside environment and pass them
on to the brain through the network
of nerves in the body.
The brain, the spinal cord and the
nerves form the nervous system.
Nerves are like telephone wires that
link every part of the cells or neurons
which are connected to each other.
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NERVE CELLS
You know that your hair and
nails, grow gradually. As they
grow, their upper part
becomes dead. So, there are
no neurons present in them.
This is why we do not feel any
sensation while cutting them.
The brain is like a telephone
exchange where messages are
sent and received through the
nerves. The spinal cord can be
compared to a bundle of
telephone lines inside a
telephone cable.
Brain
Nerves
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THE BRAIN
Cerebrum
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THE MEDULLA
It is also called the brain
stem. It is situated at the
base of the brain and joins
the spinal cord.
It controls involuntary
actions of the body such
as breathing, the
heartbeat and the working
of many internal organs.
Voluntary actions are those actions
that are under our control while
involuntary actions are those actions
that we cannot control. For example,
the beating of our heart.
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The spinal cord is a thick
bundle of nerves.
It extends from the medulla of
the brain to almost the end of
the spine. Several nerves
branch out from the spinal cord
to all parts of the body. The
spinal cord links the brain with
the rest of the body and also
controls reflex actions.
Wizard’s Corner
The brain can store about
100 million bits of
information in a lifetime.
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THE SPINAL CORD
Messages travel
from the sense
organs to the brain
and from the brain
to the spinal cord, to
all parts of the body,
through the nerves.
For example, when
the telephone bell
rings, the ear, our
sense organ -
receives the
message in the form
of sound waves.
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NERVES
This message is then transmitted to the brain
through nerves. The brain interprets the
message and sends the order. A message is
sent back through the nerves to the muscles
of the hand that was used to lift the receiver.
Sensory nerves carry messages from
the sense organs to the spinal cord, or
the brain.
Motor nerves carry messages from the
brain or the spinal cord to the muscles.
Connecting or mixed nerves carry
messages to the brain or spinal cord
and bring orders from the brain.
A network of nerves runs throughout the body.
Nerves link every part of the body to the brain
through the spinal cord. Our body has three
kinds of nerves –sensory, motor and mixed.
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1
2
3
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NERVES
The nervous system helps in
controlling all our actions. We
cannot read, write, learn,
dance, play, eat and go to
school without the functioning
of the nervous system of our
body.
Apart from the regular actions,
some of our sudden actions are
also controlled by our nervous
system. Such actions are
known as reflex actions.
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REFLEX ACTION
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Reflex actions are sudden,
involuntary actions in response to a
stimulus. A stimulus is any change in
the external or internal environment
of an organism.
For example, if you touch a hot
object, you withdraw your hands
quickly or, if you see your favourite
food, your mouth waters. Messages
to carry out such actions do not reach
the brain as they are transmitted
through the spinal cord. So, we do
not need time to think about these
actions as they happen instantly.
REFLEX
ACTIONS
REFLEX
ARC
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REFLEX ACTION
We become aware of our surroundings
by seeing, hearing, feeling, etc. We use
our senses to obtain information about
our environment.
The sense organs are, thus, our
windows to our world. These include
the eyes, the ears, the nose, the skin
and the tongue.
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SENSE ORGANS
We get most of the information
about the environment through
our eyes. Eyes are considered as
the most important sense organ.
The eyes are set into the eye
socket in the skull. Our eyelids and
eyelashes protect our eyes from
dirt, strong light, and injuries.
The eyes are connected to the
brain by the optic nerve that
carries the message to the brain,
and the brain tells us what we are
looking at.
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1
2
3
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THE EYES
The cornea, the first layer, is transparent.
The second layer is coloured and is called
the iris. The black spot in the centre of
the iris is the pupil. Tiny muscles control
the size of the pupil depending on the
amount of light the eyes are exposed to.
If there is less light, the pupil
automatically becomes bigger to take in
more light; and if the light is bright, the
pupil becomes smaller to take in less
light.
The third layer is the retina. It acts as a
‘screen’ on which the image of an object
is formed for us to see it.
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PARTS OFANEYE
Eyeballs, which rest on a pad of fat have three main layers.
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2
3
The light coming from an
object passes through the
cornea and goes to the pupil.
Behind the pupil is a lens that
helps in focusing the light.
When the light rays fall on the
retina, the nerve cells in the
retina send a signal to the
brain through the optic nerve.
The image formed on the
retina is inverted and the
brain processes it in such a
way that you perceive the
image as right side up.
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HOW DOEYES WORK?
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The ears have two functions –
hearing and maintaining the balance
of the body. The external ear acts like
a funnel and collects the sound waves
(sound travels in the form of waves).
The sound waves go to the middle
part of the ear, which has the ear
drum, and three small bones that
help in the transmission of sound.
The sound waves are then sent to the
inner ear, where they are converted
into electrical signals by the nerves
and sent to the brain, which
interprets the message received.
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EARS
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The nose helps us to smell. You
know that every time we
breathe in, air flows into our
nose. The neurons present in
the nose are sensitive to smell.
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THE NOSE
We can sense the smell of
different things because of the
particles that they are made up of.
When these particles meet the nerve cells in the nose, they
send the message to the brain. It then interprets the message
as the smell of the substance. The sense of smell and taste are
linked. When food smells good, we want to eat it.
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The tongue helps us to taste.
The tongue has thousands of
taste buds which have nerve
endings that carry messages
to the brain.
Wizard’s Corner
The snake uses its tongue to smell things
that is why, it keeps sticking out its tongue.
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THE TONGUE
We can sense five types of taste –
sweet, sour, salty, bitter and umami.
The taste buds are grouped together,
in different areas of the tongue.
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The skin covers the entire body. It helps protect the internal organs of
the body. It has millions of nerve endings that can detect sensations
such as pain, pressure, heat and cold. The nerves carry these messages
to the brain.
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THE STRUCTURE OF THE SKIN
The skin also has millions
of tiny holes or sweat
pores, which allow sweat
to come out. Sweat
contains body wastes.
Thus, the skin helps in
cleaning the body. The skin
also contains oil glands
that release oil. This keeps
our hair flexible and makes
the skin waterproof.
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So, what can you do for your brain?
Eat healthy foods which contain
potassium and calcium, two minerals that
are important for the nervous system.
Get a lot of playtime (exercise).
Wear a helmet when you ride your bike
or play other sports that require head
protection.
Use your brain by doing challenging
activities, such as puzzles, reading,
playing music, creating art, or anything
else that gives your brain a workout!
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BEGOOD TOYOUR BRAIN
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The brain, spinal cord and the nerves form the nervous system.
The brain has three parts: the cerebrum, the cerebellum and
the medulla. Each has a specific function.
There are three kinds of nerves –sensory, motor and mixed.
The spinal cord runs down from the medulla to the lower back.
A reflex action is a sudden action which is under the control of
the spinal cord.
We get information about our surroundings through the sense
organs which are, eyes, ears, nose, skin and tongue.
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2
3
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6
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KEEP INMIND
Brain: control centre of the body
Nerves: structures that carry messages from one part of the
body to another
Reflex action: an involuntary action in response to a stimulus
Taste buds: structures on the surface of the tongue that help us
to detect various tastes
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VOCABULARY
